Electronic governor having an overspeed preventing circuit for internal combustion engines

ABSTRACT

In an electronic governor for internal combustion engines, in which the output voltage of a comparison circuit comparing the output voltage in proportion to the rotative speed of the engine with the output voltage responding to the position of an accelerator lever is conducted to the control coil of a fuel regulating rod in a fuel injection pump, and the position of said fuel regulating rod is electromagnetically controlled by the generated electromagnetic force, there is provided an overspeed preventing circuit arranged to reverse the direction of the electromagnetic force produced in said control coil when the output voltage from another speed sensing circuit exceeds a constant value.

United States Patent [1 1 Ohtani et al.

[451 June 19, 1973 ELECTRONIC GOVERNOR HAVING AN OVERSPEED PREVENTING CIRCUIT FOR INTERNAL COMBUSTION ENGINES [75] Inventors: Yoshio Ohtani,

Higashi-Matsuyama, Todomu Kakijima, lruma-gun, both of Japan [73] Assignee: Diesel Kiki Kabushiki Kaisha,

. Tokyo, Japan [22] Filed: Mar. 1, 1971 [21] Appl. No.: 119,635

[30] Foreign Application Priority Data Mar. 6, 1970 Japan 45/21330 [56] References Cited UNITED STATES PATENTS l-lofmann 123/102 Primary Examiner-Laurence M. Goodridge Assistant Examiner-Ronald B. Cox Att0rney-Larson, Taylor and Hinds [57] ABSTRACT In an electronic governor for internal combustion en gines, in which the output voltage of a comparison circuit comparing the output voltage in proportion to the rotative speed of the engine with the output voltage re sponding to the position of an accelerator lever is conducted to the control coil of a fuel regulating rod in a fuel injection pump, and the position of said fuel regulating rod is electromagnetically controlled by the generated electromagnetic force, there is provided an overspeed preventing circuit arranged to reverse the direction of the electromagnetic force produced in said control coil when the output voltage from another speed sensing circuit exceeds a constant value.

1 Claim, 1 Drawing Figure ELECTRONIC GOVERNOR HAVING AN OVERSPEED PREVENTING CIRCUIT FOR INTERNAL COMBUSTION ENGINES This invention concerns an electronic governor for internal combustion engines, in which the quantity of fuel supply is controlled by comparing two output voltages, one being proportional to the rotative speed of the engine and the other being in correspondence with the current position of accelerator lever and by applying the output voltage resulting from said comparison to the control coil of a fuel regulating rod in a fuel injection pump, so that said coil develops an electromagnetic force to position said rod against the counterforce exerted by the governor spring.

Electronic governors of this type began to be developed in recent years because of the potentiality of this type for the excellence of its control performance. There is one drawback inherent in this type, however, in that deterioration in performance of electrical parts, circuit maloperation, or breakage or weakening of such mechanical parts as springs, if any, may prevent said control coil of the fuel regulating rod from getting deenergized, causing an electric current to keep on flowing in said coil to defeat the governor action and thus forcing the engine to overspeed. The probability of such an overspeeding is small but, should it occur once, it would seriously shorten engine life or, worse, destroy the engine beyond repair.

An object of this invention is to eliminate said drawback by detecting the engine speed by means of another speed sensing circuit separate from the one included in the electronic governor network and by controlling the fuel regulating rod according to the detected speed.

In order that this invention may be more readily understood it will now be described, by way of example only, with reference to the accompanying drawing which is a circuit diagram showing an electronic governor for internal combustion engines, equipped with an overspeed preventing circuit according to this invention.

In the diagram shown, A is a conventional electronic governor circuit, and B is the overspeed preventing circuit having a Schmitt circuit. Elements T,, T, and T are transistors; elements R, through R,,, inclusive, are resistors; elements C, and C capacitors; elements D, and D diodes; and elements L, and L coils for detecting engine speed. Element L is a fuel regulating rod control coil of a fuel injection pump not shown; element r is a relay, r, and r being normally-closed contacts and r, and r, being normally-open contacts; lines 1 and 2 are a positive and a negative conductor, respectively, in that order.

Coil L, of circuit A" detects engine speed. By this detection, the electromagnetic force developed by control coil L, on fuel regulating rod is changed to control I the fuel regulating rod, not shown. in circuit B", normally-closed contacts r, and r, in relay r are connected to said control coil L Coil L also detects engine speed, just as does coil L,, and develops a corresponding voltage. This voltage is converted by capacitor C, and diode D, into a DC voltage proportional to the rotative speed of the engine. The Schmitt circuit, comprising transistors T, and T, and resistors R through R,,, amplifies the DC voltage. Since transistor T is inverted relative to T, in phase relationship, a rise in engine speed causes transistor T, to switch on and transistor T to switch off, thereby de-energizing relay r.

In the circuit arranged as above, the overspeed preventing function is performed in the following manner: When engine speed rises due to some malfunctioning occurring in the governor circuit, transistor T, becomes conductive, so that transistor T which has been conducting, becomes non-conductive to de-energize relay r, and normally-closed contacts r, and r close. This reverses the flow of current through control coil L on said fuel regulating rod, not shown, and also the magnetic polarity of said coil L relative to a permanent magnet located within itself, so that the fuel regulating rod receives a pull in the direction for decreasing fuel supply, due to two forces, one being that of the governor spring, not shown, and the other being that of coil L whose reversed magnetic direction coincides with that of the spring force. By this pull, consequently, the fuel regulating rod shifts its position to prevent the engine from overspeeding into the critical range. Even when the governor spring accidentally breaks, the reversed electromagnetic pull of coil L moves the fuel regulating rod in the anti-overspeed direction to avoid the overspeeding of the engine.

The operating point of this circuit, or the engine speed at which the circuit is to start operating as above, can be set by adjusting the potential of the base of transistor T, by means of variable resistor R,.

As the engine speed falls, relay r becomes energized again, closing normally-open contacts r, and r, and allowing the fuel regulating rod to move back in the direction for increasing fuel supply, thereby raising engine speed. The operator or driver by this time cannot but realize the abnormal condition and will therefore turn off the power source of the governor to stop the engine for inspection or repair.

It will be obvious from the foregoing description that the electronic governor for internal combustion engines, according to this invention, is a fail-safe device in that the accidental failure, if any, of the governor spring does not defeat the overspeed preventing function and that an open-circuiting of the speed-sensing coil in the governor does not result in loss of said function because the overspeed preventing circuit is independent of the governor circuit and has its own speedsensing coil. Thus, the governor according to this invention is practical and signifies an improvement.

While this invention has been described in detail with respect to its preferred embodiment it is to be understood that various changes and modifications may be made without departing from the spirit and scope of this invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. An electronic governor for an internal combustion engine comprising a comparison circuit for comparing a first input voltage proportional to the rotational speed of the engine and a second input voltage related to the position of an accelerator operating lever and for producing an output 'voltage in accordance therewith, means for connecting the output of said comparison circuit to the control coil of a fuel regulating rod of a fuel injection pump so that the position of the fuel regulating rod is electromagnetically controlled in accordance with the electromagnetic force generated by the control coil responsive to the output of said comparison circuit, and an overspeed circuit for preventing engine overspeed including a further, separate voltage generating circuit for generating a D.C. output voltage proportional to the rotational speed of the engine and means for connecting the output of said D. C. voltage generating circuit to said control coil so as to produce an electromagnetic force which acts in an opposite direction to the said electromagnetic force produced by the output of said comparison circuit when the rotational speed of the engine exceeds a predetermined value, said connecting means including means responsive to said DC. voltage for disconnecting said comparison circuit from said control coil and for connecting said D.C. voltage generating circuit to said control coil when said D.C. output voltage of said voltage generating circuit exceeds a predetermined value, said switching means comprising a relay and first and second pairs of switching contacts controlled by said relay, said first pair of contacts being closed responsive to the energization of said relay to connect the output of said comparison circuit to said control coil and the second pair of relay contacts being closed responsive to the deenergization of said relay to connect said voltage generating circuit to said control coil, and said voltage generating circut including sensing coil means for sensing the rotational speed of the engine and for producing an output voltage in accordance therewith, means for converting the output voltage produced by said sensing coil means into a corresponding D.C. voltage, and transistor amplifier means including a first transistor, connected to said converting means, which conducts responsive to the said D.C. voltage produced by said converting means exceeding a predetermined value and a second, normally conducting transistor which is rendered non-conducting when said first transistor conducts, and means for connecting said second transistor in series with said relay so that said relay is deenergized when said second transistor is rendered nonconducting. 

1. An electronic governor for an internal combustion engine comprising a comparison circuit for comparing a first input voltage proportional to the rotational speed of the engine and a second input voltage related to the position of an accelerator operating lever and for producing an output voltage in accordance therewith, means for connecting the output of said comparison circuit to the control coil of a fuel regulating rod of a fuel injection pump so that the position of the fuel regulating rod is electromagnetically controlled in accordance with the electromagnetic force generated by the control coil responsive to the output of said comparison circuit, and an overspeed circuit for preventing engine overspeed including a further, separate voltage generating circuit for generating a D.C. output voltage proportional to the rotational speed of the engine and means for connecting the output of said D. C. voltage generating circuit to said control coil so as to produce an electromagnetic force which acts in an opposite direction to the said electromagnetic force produced by the output of said comparison circuit when the rotational speed of the engine exceeds a predetermined value, said connecting means including means responsive to said D.C. voltage for disconnecting said comparison circuit from said control coil and for connecting said D.C. voltage generating circuit to said control coil when said D.C. output voltage of said voltage generating circuit exceeds a predetermined value, said switching means comprising a relay and first and second pairs of switching contacts controlled by said relay, said first pair of contacts being closed responsive to the energization of said relay to connect the output of said comparison circuit to said control coil and the second pair of relay contacts being closed responsive to the de-energization of said relay to connect said voltage generating circuit to said control coil, and said voltage generating circut including sensing coil means for sensing the rotational speed of the engine and for producing an output voltage in accordance therewith, means for converting the output voltage produced by said sensing coil means into a corresponding D.C. voltage, and transistor amplifier means including a first transistor, connected to said converting means, which conducts responsive to the said D.C. voltage produced by said converting means exceeding a predetermined value and a second, normally conducting transistor which is rendered nonconducting when said first transistor conducts, and means for connecting said second transistor in series with said relay so that said relay is de-energized when said second transistor is rendered non-conducting. 